Impacts of land use/cover changes on surface climate over east Asia for extreme climate cases using RegCM2

[1] Systematic biases were found in the National Center for Atmospheric Research Regional Climate Model (NCAR RegCM2) through the 10-year east Asian summer simulations. In the simulations, positive and negative surface temperature biases of 2degrees-4degreesC occurred systematically over north China and Mongolia. The model also produced excessive precipitation over land but less precipitation over the southern ocean of the model domain. In this study, impacts of land cover changes (LCC) on the systematic biases were investigated through the cool/wet and warm/dry summer climate simulations using two types of land cover maps using RegCM2. One type was an NCAR land cover map, and the other was a current land cover map derived from satellite data. Simulated latent heat flux and wind speed increased noticeably over central and north China, where deciduous broad leaf trees have been replaced by mixed farm and irrigated crop. As a result, the systematic positive biases over central and north China were greatly reduced regardless of climate regimes. Cooling in central and north China resulted in a pressure gradient decrease between the east Asian continent and the Pacific Ocean. The decrease in pressure gradient suppressed northward transport of moisture from south China and the South China Sea. The change reduced not only excessive precipitation over north China and Mongolia but also less precipitation over south China. However, in LCC, precipitation increased in the Korean Peninsula and the Japan Islands, in particular, during July and August. As a result, LCC resulted in cooler and drier summer climate over north China, but cooler and wetter summer climate over the Korean Peninsula and the Japan Islands irrespective of climate regimes. In general, the impacts of LCC were relatively significant in the warm and dry summer.